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Fast calculating formulas of current passing through grounding system of high voltage substation when lightning strikes at the grounding wire of transmission line

Current injecting a grounding system of high voltage substation decides the amplitude and the voltage distribution along the grounding grid [1]-[2]. Therefore, the determination of short circuit current at substation is always cared by the designers. This paper presents a method to fast calculate the current passing through grounding system of high voltage substation when lightning strikes at the grounding wire of transmission line. | Science & Technology Development, Vol 11, No.09 - 2008 FAST CALCULATING FORMULAS OF CURRENT PASSING THROUGH GROUNDING SYSTEM OF HIGH VOLTAGE SUBSTATION WHEN LIGHTNING STRIKES AT THE GROUNDING WIRE OF TRANSMISSION LINE Ho Van Nhat Chuong University of Technology, VNU-HCM (Manuscript Received on September 21st, 2007, Manuscript Revised May 27th, 2008) ABSTRACT: Current injecting a grounding system of high voltage substation decides the amplitude and the voltage distribution along the grounding grid [1]-[2]. Therefore, the determination of short circuit current at substation is always cared by the designers. This paper presents a method to fast calculate the current passing through grounding system of high voltage substation when lightning strikes at the grounding wire of transmission line. 1. INTRODUCTION To calculate the current of lightning exactly, we must not only apply numerical analysis but also use computer. This problem requires that users need to have professional knowledge and the ability of programming or using specialized software that are very expensive. Thus, this paper presents some new formulas to calculate the current passing through grounding system of high voltage substation when lightning strikes at the grounding wire of transmission line. Fig 1. Equivalent circuit of grounding wire line Based on transmission line models [3]-[5], the grounding wire system can be modeled as equivalent circuit (Fig.1). Where, n is the number of span, each span is represented by a picircuit. The shunt impedance Zp is the grounding impedance of pole and the series impedance Zs is the impedance of grounding wire (if the transmission line has two grounding wires then this series impedance will be Z s / 2 ). Z1 is the impedance of grounding system of the first substation and Z2 is the impedance of grounding system of the second substation. In case of open-ended grounding wire line, Z2= ∞. The system of grounding wire and impedance of pole can be modeled as a series